U.S. Pat. No. 9,274,266 describes a solar concentrator that contains an array of focusing lenses and a corresponding array of convex focusing mirrors. The combination of refractive lenses and reflectors is known as catadioptric pairs. Between the lenses and mirrors at the focal plane is a movable transparent lightguide having an array of angled reflector elements, where there is one angled reflective element per pair of lenses and focusing mirrors. When the focal spots of the lenses/mirrors fall upon the reflector elements, the light is optimally deflected into the lightguide and is trapped by total internal reflection (TIR) until the light exits an edge of the light guide. Photovoltaic (PV) cells are attached along the edge of the lightguide. The lightguide is translated laterally so that the reflector elements remain aligned with the focal spots as the angle of incident sunlight changes over time so there is a maximum of light that is emitted by the edge of the lightguide.
A related prior art solar concentrator (described in Nature Communications, DOI:10.1038/ncomms7223, Entitled Wide-Angle Planar Microtracking for Quasi-Static Microcell Concentrating Photovoltaics, 2015, by Price et al.) contains an array of top focusing lenses and bottom focusing mirrors, forming catadioptric pairs. The array of catadioptric pairs provides an array of focal spots, and the catadioptric pairs are optimized so that the focal spots remain substantially in a single plane as the angle of incident sunlight varies over a wide range. A corresponding array of photovoltaic cells on a moveable sheet translates at the focal plane of the catadioptric pairs by microtracking so that the focal spots of the catadioptric pairs remain aligned with the photovoltaic cells as the angle of incident sunlight changes over time.
A drawback of the two systems described above is that they require movement of the entire lightguide (including the PV cells at the lightguide output) or PV sheet relative to the catadioptric pairs. This requires external moving parts, subject to degradation in the environment. A further limitation of both prior art systems is that the designs are solely intended for electricity generation and do not contemplate the harvest of concentrated light for interior illumination.
What is needed is a sunlight collection and concentration system that is highly robust, requires minimal control systems, is very flexible in its implementation, and provides high-quality sunlight for interior illumination.